Th=
is
article was previously published under Q140060
Wh=
en you
access a floppy disk, you may receive one of the following error messages: =
A:\
is not accessible.
The device is not ready.
-<=
span
class=3DGramE>or-
Disk
is not formatted
The disk in drive A is not formatted.
Do you want to format it now?
-<=
span
class=3DGramE>or-
STOP:
The disk media is not recognized, it may not be formatted.
Th=
e same
disk may work correctly with MS-DOS or Windows 95, or after you re-format t=
he
disk with Windows 98, Windows Millennium Edition, Windows NT, Windows 2000,
Windows XP, or Windows Server 2003.
Th=
is
problem occurs on disks that do not contain a media descriptor byte in the =
BIOS
parameter block (BPB) of the boot sector. Some older preformatted floppy di=
sks
do not contain a media descriptor byte. Older product disks may also not ha=
ve
the media descriptor byte.
The media descriptor indicates the type of medium currently in a drive. With
MS-DOS and Windows 95, you do not have to set the media descriptor byte.
Therefore this problem does not occur with these older operating systems. <=
br>
The media descriptor byte is located in the BPB of the boot sector at offse=
t 21
(15h) and in the first byte of each FAT on the disk.
To=
resolve
this problem, re-format the floppy disk with Windows 98, Windows Millennium
Edition, Windows NT, Windows 2000, Windows XP, or Windows Server 2003.
Warning: This workaround is for adva=
nced
users only. This workaround involves using a disk sector editor to modify t=
he
media descriptor byte on the floppy disk. Misuse of a disk sector editor may
make all the data on the drive or volume permanently inaccessible. Disk sec=
tor
editors function at a level "below" the file system, so the typic=
al
checks for maintaining disk consistency do not apply. This provides you dir=
ect
access to every byte on the physical disk regardless of access credentials.
Therefore, you can damage or permanently overwrite critical on-disk data
structures. Use this workaround at your own risk.
To work around this problem, use a disk sector editor to change the BPB med=
ia
descriptor byte to the appropriate value. For example, you can use the DiskProbe tool to do this on a Windows NT 4.0-based,
Windows 2000-based, Windows XP-based, or Windows Server 2003-based computer=
. DiskProbe (Dskprobe.exe) is included with the Windows
Support Tools for Windows XP Professional and Windows XP 64-Bit Edition, the
Windows 2000 Support Tools, and Windows NT 4.0 Resource Kit Support Tools.<=
br>
The following table lists the most common media descriptor bytes:
Byte Capacity Media Size and Type
-------------------------------------------------
F0 2.88 MB 3.5-inch, 2-sided, 36-=
sector
F0 1.44 MB 3.5-inch, 2-sided, 18-=
sector
F9 720K 3.5-=
inch,
2-sided, 9-sector
F9 1.2 MB 5.25-inch, 2-sid=
ed,
15-sector
FD 360K 5.25=
-inch,
2-sided, 9-sector
FF 320K 5.25=
-inch,
2-sided, 8-sector
FC 180K 5.25=
-inch,
1-sided, 9-sector
FE 160K 5.25=
-inch,
1-sided, 8-sector
FE 250K 8-in=
ch,
1-sided, single-density
FD 500K 8-in=
ch,
2-sided, single-density
FE 1.2 MB 8-inch, 2-sided,
double-density
F8 ----- Hard disk<= o:p>
=
&nb=
sp;
Th=
e BPB
media descriptor byte is located in sector 0 of the disk, and looks similar=
to
this:
addr data:
0000 EB 3C 90 4D 53 44 4F 53 35 =
2E 30
00 02 01 01 00
0010 02 E0 00 40 0B F0 09 00 12 =
00 02
00 00 00 00 00
=
&nb=
sp;
xx <---- This byte above XX is the med=
ia
descriptor byte and is at offset hexadecimal 21 (15h).
=
&nb=
sp;